Haven't had FSD's, but I too did exhaustive research before making the call to go with Yellows. I spoke with several members who have recently (within 5 months) put FSD's on their cars. The general feeling is simple. Yellows for more performance minded driving, FSD for more soft and cushy ride. Most people who have them always say the car feels really, really soft (something I personally don't like, even on the interstate) and they wish the normal driving was slightly firmer. Around corners though they say they firm up nicely. But honestly, there is no free lunch. I should also mention both people I talked to bought the FSD/Eibach spring kit and didn't re-use stock springs as I did with the yellows.

I am sure you'll be happy with either as they both are light years ahead of the stock units IMO. I don't know if you have seen this, but here is a test of both. http://www.tirerack.com/suspension/tests/koni_fsd.jsp. While I thought it was a good article I'll restate the benefits of the yellows after some 15k miles of driving with them installed.

1. Adjustability. After a couple thousand miles of break in I was able to firm them up slightly as they began to feel a little softer than when new. I am sure I can continue this throughout their life span and keep them performing as I like right until they need to be replaced. Adjustments aren't hard, the link to youtube in my sig has a video on it.

2. Performance. They handle better than I expected, even when really firm. A BMW 3'er is a sport sedan, not a luxury sedan (that is what the 5 and 7 series are for) so I do not believe in a soft ride ever. I log a lot of miles (30k miles since Jan 1st) and can say I feel very confident with my setup on the interstate and it handles well over long trips.

3. Lifetime warranty. When they wear out, send em to Koni, they rebuild them and send em back. Thank you Koni!

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